1. Field of the Invention
The present invention relates to an electron beam excitation ion source.
2. Description of the Related Art
Strong demand has arisen for developing an ion source having a large current and a long service life in, e.g., an ion-implantation apparatus utilized for manufacturing semiconductor devices.
The present applicant proposed ion beam excitation ion sources each for ionizing a source gas with an electron beam in Published Unexamined Japanese Patent Application No. 61-290629 and Japanese Patent Application No. 61-121967.
In such an electron beam excitation ion source, electrons are extracted from a plasma formed by a glow discharge and are accelerated. The accelerated electrons are guided to an ion generation chamber having a source gas atmosphere for generating a predetermined type of ions. The electrons are bombarded against source gas molecules to generate a plasma. Ions are then extracted from the plasma through an ion extraction slit formed in the ion generation chamber. This ion source has an advantage in that a high ion current density can be obtained by low ion energy.
Further demand has arisen for increasing an ion current density to shorten a processing time and increase a throughput even in the electron beam excitation ion source described above.